Crystal structure and chemical composition of Li-, Fe-, and Mn-rich micas

We present in this paper the crystal chemical characterization of three (Fe, Mn)-rich lithian trioctahedral micas. The samples are from Hirukawa mine (Japan) (unit formula: [iv](Si3.425Al0.575)4.00[vi](Al1.002Ti0.002Cr0.001Fe0.379Mg0.005Mn0.173Li1.438)3.00 [xii](Ca0.002Ba0.001Na0.049K0.948Rb0.002)1.00 O10F2 ; unit-cell dimensions: a = 5.264(1), b = 9.086(2), c = 10.099(3) Å, β = 100.719(5)°, V = 474.6(2) Å3); from Mokrusha mine (Russia) (unit formula: [iv](Si3.304Al0.696)4.00 [vi](Al1.004Ti0.001Fe0.362Mg0.005 Mn0.306Li1.322)3.00 [xii](Ca0.012Ba0.001Na0.042K0.940Rb0.005)1.00 O10F2; unit-cell dimensions: a = 5.297(5), b = 9.133(7), c = 10.168(9) Å, β = 100.78(2)°, V = 483.2(7) Å3); and from Sawtooth Mountains (Boise County, Idaho, U.S.A.) (unit formula: [iv](Si3.105Al0.895)4.00 [vi](Al0.913Ti0.018 Fe0.456Mg0.031 Mn0.521Li1.061)3.00 [xii](Ca0.004Ba0.003Na0.048K0.924Rb0.021)1.00 O10F2; unit-cell dimensions a = 5.2984(3), b = 9.1461(6), c = 10.0966(7) Å, β = 100.818(4)°, V = 480.58(5) Å3). All crystals belong to 1M polytype with layer symmetry C12(1) and show M1 and M3 sites much greater than M2. Moreover mean electron count values are much more variable for M1 and M3 sites than for M2. Unlike sample from Sawtooth Mountains, tetrahedral mean bond lengths appear to be smaller for T1 than for T11 site in Hirukawa mine and in Mokrusha mine.When compared to samples from the zinnwaldite series, crystals under study show similar crystal chemical trends, thus hinting to similar effects produced on layer structure by Fe and Mn cations.